Hello, the villain was unknown. Was 2nd barrelling the best option here? After the call I really just thought the villain was on a draw or Qx at best so my instinct is to bluff bet the river, but this always seems to get me in trouble with unknowns because they might just call any pair even on the river.

Generally speaking when the turn pairs like this, it is a bad spot to keep bluffing. Why? Because Villain hand strength has changed. i.e if he has Qx he still has top pair, if he has 66-JJ he still has 2nd pair etc...
So basically if he called flop he will often call turn again.

Obviously so could argue that he could be on a flush draw too. but since we don't have any info on villain it is best to check back OTT. Remember btw that vs his flush draw you are ahead so you can still win the pot!

So I would check back on the turn.

As played I wouldn't bet the river because imo he is not folding anythin that he has called flop and turn with and again you beat his FD.

You should start from the sizing in first place cause you wouldn't do such a size with a made hand, Bet the flop bigger and gain the fold equity which is needed. He ain't folding any hands vs your sizing there even the weakest pairs and maybe even Ace high may float vs you.

Nor the turn or River ain't good for 2nd/3rd barrel cause he isn't going to fold that much vs your line, rather Check it behind.